The present invention relates to Ground Penetrating Radar (GPR) systems, and more particularly, to timing within GPR systems.
GPR systems often comprise at least one transmitter that transmits an electromagnetic impulse. The transmitted impulse may reflect off of a buried object to create a reflected electromagnetic waveform. At least one receiver may receive the reflected waveform to collect information about the object. Difficulty arises, however, in accurately scheduling the time when each transmitter transmits an impulse signal and when each receiver samples a received waveform.
U.S. Pat. No. 6,496,137 to Johansson, which is herein incorporated by reference for all that it contains, describes a GPR timing system comprising a control circuit that receives a transmit timing input signal and a receive timing input signal. The system delays the transmit timing input signal and generates a number of intermediate transmit timing signals delayed with respect to each other by a delay time, selects either the transmit timing input signal or a corresponding one of the intermediate transmit timing signals as a corresponding output transmit timing signal, delays the receive timing input signal and generates a number of intermediate receive timing signals delayed with respect to each other by the delay time, adds the delay time to the intermediate receive timing signals, and selects either the receive timing input signal or a corresponding one of the intermediate receive timing signals as a corresponding output receive timing signal.
U.S. Pat. No. 5,835,054 to Warhus, et al., which is herein incorporated by reference for all that it contains, describes how the accuracy of a calculation of distances using a GPR system depends on how precisely a time-delay of echoes can be measured. Ideally, each returned echo is a scaled and time-shifted version of the transmitted pulse. Thus, a reference point on the pulse can be used to calculate the time-delay, e.g., either the leading or trailing edge of the pulse. In the presence of noise, however, such reference points can be hard to determine. Correlation or inverse filtering of the incoming signal with the transmitted pulse can be used to produce a peak at the time-delay of the echo and provide a reference point that is much easier to locate.
Despite these advances, simplified means for timing GPR systems is desirable.